Improves comms around project ethos

[devmoran]

• New copy on index to explain the high-level ethos of the project

[devmoran]

Updated to address PR comments.
@TomHennen I'd like to get this merged in so that we can lock this up with #134. If you're happy, pls review and merge.
If we feel there's further improvements to make we can always raise another PR.

[TomHennen]

This looks good to me, but I'd like someone outside Google to review since it is adjusting the mission statement.

@inferno-chromium added @joshuagl to provide that review.

[inferno-chromium]

Adding all the goverance board members
@joshuagl
@mlieberman85
@trishankatdatadog
@david-a-wheeler
@MarkLodato (ooo)
@zakgreant
@brunodom

[inferno-chromium]

@devmoran - you would need to rebase after last commit.

[joshuagl]

Thanks for the ping, I'm a bit behind after a long weekend AFK. This LGTM and in-line with the mission we discussed in the recent community meeting.

I added a suggestion to mention that we want SLSA to be automatically verifiable.